In clinical testing for evaluating the state of illness, and in environmental measurement for measuring the state of nitrogen oxide, ozone and the like, measurements using immunoassay and color reaction are typically used. In recent years, in those measurement methods, a measurement technique using surface plasmon resonance has been developed and come into practical use (for example, refer to Patent Documents 1 and 2). This measurement technique uses resonance between an evanescent wave and a surface plasmon wave on the surface of a metal with which a specimen of an object to be measured is in contact.
Measurement using surface plasmon resonance, as shown in FIG. 11 for example, is performed using an SPR measurement device 1, which includes a light source 2, an incident side lens 3, a prism 4, and a light detecting section 5. A square planar measuring chip 10 is fixed on a measurement face 4a, which is the top surface of the prism 4 of the SPR measurement device 1. A metal thin film (Au thin film) 11 is adhered to the substrate 10a of the measuring chip 10, as shown in FIG. 12 in detail. A specimen, being an object to be measured, is in contact with the metal thin film 11.
A light injected from the light source 2 is collected by the incident side lens 3, and the light is injected into the prism 4 and irradiated onto the measuring chip 10 on the measurement face 4a of the prism 4. The light that irradiates the measuring chip 10 passes through the substrate 10a of the measuring chip 10 as shown in FIG. 12 in detail, and is reflected by the metal thin film 11. The intensity of the reflected light is measured by the light detecting section 5 configured by an imager such as a so-called CCD image sensor or the like. By such measurement, as shown in FIG. 13, a valley is observed in which the reflection coefficient becomes extremely low at the angle at which the above resonance occurs.
As described above, in the SPR measurement device 1, light arrives at and departs the measurement face 4a of the prism 4 and the measuring chip 10. At this time, in order to suppress the refraction and reflection of the light at the boundary between the measurement face 4a and the measuring chip 10, it is necessary for the refractive indexes of the prism 4 and the measuring chip 10 to match, and to adhere the measuring chip 10 to the measurement face 4a completely.
However, even though the refractive indexes of the prism 4 and the measuring chip 10 can be matched easily by material selection or the like, it is not easy to adhere the two completely without any gap. Therefore, matching oil (refractive index matching agent) whose refractive index matches them is normally intervened between the prism 4 and the measuring chip 10. By so doing, refraction and reflection of the light in the boundary between the prism 4 and the measuring chip 10 are suppressed.
Normally, in SPR measurement, antibodies and DNA conditional on the objective substance to be detected, are fixed in advance on the metal thin film 11 of the measuring chip 10. When a specimen solution in which the objective substance exists is introduced into the chip, the objective substance is captured by the stabilized substance, and detected as a signal change of the SPR measurement device 1. It is not easy to desorb the objective substance once captured by the stabilized substance completely, and accurate measurement is difficult in repeated measurements using the same measuring chip 10. Especially, in the case where medical treatment or food evaluation is intended, in order to avoid contamination between specimens, it is desirable to use the measuring chip 10 only once. From this point, the frequency of exchange of measuring chips 10 with respect to the SPR measurement device 1 is extremely high.
Incidentally, in the case where the measuring chip 10 is adhered using matching oil, it is not easy to remove the measuring chip 10 from the SPR measurement device 1. Furthermore, it is also not easy to remove the matching oil completely from the measuring chip 10 and the measurement face 4a of the prism 4.
Therefore, it is not possible to exchange measuring chips 10 smoothly, which hinders efficient measurement. Moreover, it is necessary to use a matching oil absorber in order to remove the matching oil. Consequently problems occur in terms of cost and waste management.
Therefore, in order to deal with this, Patent Document 3 proposes a method for fixing the measuring chip 10 on the SPR measurement device 1 using matching film instead of matching oil.